Tubing manufacture



Sept. 5, 195 w. E. MEISSNER TUBING MANUFACTURE Filed March 12, 1965 United States Patent O 3,340,338 TUBING MANUFACTURE William E. Meissner, Devon, Pa., assignor to FMC Corporation, Philadelphia, Pa., a corporation of Delaware Filed Mar. 12, 1965. Ser. No. 439,299 Claims. (Cl. 26489) The invention relates to the manufacture of tubes and film, and particularly to an improved method and appara tus for shaping a plasticized material into the form of a seamless tube or film.

In my United States Patent 3,013,311 I have disclosed a method for making tubes, films, and like articles by containing a fluid charge within a plasticized material positioned within a liquid bath, and thereafter drawing the plasticized material through the liquid bath and relative to the contained fluid charge to thereby shape the same into a desired tube form. The plasticized material of the formed tube is then set and collected. While my patented method is adapted for use with a variety of plasticized or film forming materials, the plasticized materials employed must have a density which is greater than that of the sur rounding bath. This particular condition, of course, restricts the choice of liquids which may be employed with any particular plasticized material and, in the case of the less dense materials, such as polypropylene, makes satisfactory tube forming extremely difiicult if not impossible. Accordingly, a primary object of the present invention is to provide a new or generally improved and more satisfactory method and apparatus for making tubes and like articles.

Another object of the invention is the provision of an improved method wherein a plasticized material is shaped into the form of a seamless tube by combined extrusion and drawing operations.

Still another object of the invention is to provide an improved method for continuous tube manufacture wherein a plasticized material is hydraulically shaped into a seamless tube of desired and uniform wall thickness.

A further object of the invention is the provision of a method wherein a plasticized material is drawn through a liquid bath which is of greater density than the plasticized material and relative to a contained fluid charge to effect shaping of the same into a seamless tube which is then slit longitudinally for forming a flat film.

A still further object is to provide an improved simple and compact apparatus for making continuous seamless tubes.

These and other objects and advantages of the invention will be apparent from the following description and accompanying drawing in which:

FIGURE 1 is a diagrammatic view illustrating an initial step in the tube-forming process of the present invention of injecting a fluid charge into a mass of plasticized material;

FIGURE 2 is a diagrammatic view showing the shaping of a plasticized material into a tube by the contained fluid charge and a surrounding bath;

FIGURE 3 illustrates a View showing the use of a contained fluid charge of less density than the liquid of the surrounding bath; and

FIGURE 4 is a view similar to FIGURE 3 showing the use of a contained fluid charge of greater density than the liquid of the surrounding bath.

Broadly, the manufacture of tubes or like articles in accordance with the present invention is achieved by containing a fluid charge Within a mass of plasticized material 1 positioned within a liquid bath which is of greater density than the plasticized material, and thereafter drawing the plasticized material through the liquid bath and relative to the contained fluid charge to thereby shape the 3,340,338 Patented Sept. 5, 1967 plasticized material employed.

Containment of the fluid charge is accomplished by injecting the same into the mass of flowable material, thus expanding a portion of the mass into a bulbous envelope. The withdrawal of this envelope from the liqud bath initiates the shaping of the plasticized material into a tube form and facilitates easy lacing operations. As mentioned above, and more fully described hereafter, the fluid charge serves as an internal mandrel during the tube drawing operation and therefore consists either entirely of liquid or a mixture of liquid and gas. A charge having some gas is preferred however since it assists the initially expanded portion of the buoyant plasticized material to float toward the surface of the liquid bath, and also facilitates a desired expansion of the tube as it is drawn, without any great increase in the weight of the charge itself.

While the liquid bath surrounding the mass of plasticized material may serve to set or coagulate the tube as it is formed, its primary function is to cooperate With the contained fluid charge in controlling the thickness of the tube Wall and in smoothing irregularities from the plasticized material as it is drawn from the mass. As will be more apparent hereafter, the liquid bath and fluid charge confine the plasticized material along a streamlined path as it is drawn and thus can be best visualized as together functioning as a liquid extrusion die hydraulically shaping the plasticized material into a tube form.

The apparatus for drawing the plasticized material I relative to the contained fluid charge can be of a conventional form which is best suited for the particular tube being made. When employing a fluid charge composed of liquid and gas, nip rolls or other similar means which will flatten or pinch the tube after it is formed, are preferred to prevent gas escape.

Various factors, such as the rate of drawing, the density and temperature of the liquid bath and confined fluid charge, and the character of the plasticized material have a bearing on the size of the tube which is formed. These factors thus ofifer a means whereby complete control may be exercised over the diameter and wall thickness of the tube during formation.

Throughout the description, the term liquid is intended to include both solution, such as water and oils, as well as materials, such as salts and metals, which are in amolten state at the temperature at which the present method is practiced. The terminology plasticized material as referred to above and throughout the remainder of the description and claims, denotes materials which are of less density than the surrounding liquid bath and are in a flowable, viscous, or plastic condition at and during drawing of the same into a tube form. Included within this definition are a variety of organic film-forming materials of either thermoplastic or thermosetting character, as Well as solutions, as for example of viscose, nitrocellulose, cellulose ethers and esters. Examples of thermoplastic materials sut-iable for use with the present invention include vinyl resins, such as polyvinyl acetate, copolymers of vinyl chloride and vinyl acetate, copolymers of acrylonitrile and vinyl acetate, polyacrylonitrile and copolymers of acrylonitrile with vinyl chloride, vinyl acetate, methacrylonitrile, and so forth, also polyolefines such for example as polyethylene, polypropylene, linear superpolymers of the polyester or nylon (polyamide) type, polyvinyl butyral, polyvinyl alcohols, polyvinyl ethers, while suitable thermosetting materials may include phenol aldehyde resins, urea aldehyde resins,

melamine aldehyde resins and sulfonamide aldehyde resins. The inner and outer liquids may be difl erent and reactive with each other so that they form a film at their interface, such for example as an amide and an acid of the type which will polymerize to form a polyamide film at the interface. It is to be understood that the mentioning of these particular materials is not intended to limit the invention thereto but merely to illustrate the wide variety of materials that can be used in carrying out the invention.

With reference to the drawing, the apparatus of the present invention is relatively simple and includes a tank 15 for holding a liquid bath 17, a retainer or inverted container or cup 19 positioned below the surface of the bath 17 for containing a mass of plasticized or film-forming material 21, a pipe 23 for delivering plasticized material 21 into the inverted container 19 and a conduit 25 which extends up through inverted container 19 for injecting a fluid charge into a portion of the plasticized material, as more fully described hereafter. As heretofore mentioned, the plasticized material 21 is of less density than the liquid bath 17 so that its inherent buoyancy normally retains the same up against the inside surface 27 of the inverted container 19. Preferably, the inverted container 19 is supported by the conduit 25 so that its open end has a free, smooth, and unobstructed edge 29.

During the initial stages of the method of the present invention, plasticized material 21 is delivered by the pipe 23 until it exceeds the capacity of the inverted container 19 and flows over its free edge 29. This overflow of plasticized material moves along the smooth arcuate upper surface 31 of the container 19 where it collects temporarily, as shown at 33, before floating upwardly toward the bath surface. It will be noted, however, that the plasticized material 33 remains attached to that portion of the mass which remains within the inverted container 19. A fluid charge is then injected into this accumulated portion 33 of the plasticized material through the conduit 25.

The fluid charge is of predetermined Weight and volume and preferably includes a liquid and gas, denoted by the characters 35 and 37, respectively, which may be delivered as a mixture. The character of the liquid bat-h 17 and/ or liquid portion 35 of the fluid charge will, of course, vary with the particular plasticized material employed and the desired size of the tube to be formed. In accordance with the present invention the liquid 17 is of greater density than the plasticized material 21 and for the sake of simplicity and ease of description, both of liquids 17 and 35 will be considered to be of the same density unless otherwise noted.

During the initial injection of the fluid charge, the gaseous portion 37 travels up through the liquid 35 in the pipe 25 and forms a bubble in the mass of plasticized material 21, as shown at 39 in FIGURE 1. With continued delivery of the fluid charge, the increasing volume of liquid and gas contained within the plasticized material 21 gradually expands the initially formed bubble 39 and, in effect, causes an upward flow of the plasticized material 21 to form a bulbous thin-walled envelope. During this gradual expansion of the plasticized material 21 the envelope is, of course, buoyantly elevated toward and above the surface of the bath 17 where it is maintained in an expanded form by the gaseous portion 37 of the fluid charge. As heretofore mentioned, the liquid of the bath 17 and the liquid portion 35 are of the same density and thus at this particuar equilibrium condition they assume substantially the same level, with the fluid change being completely contained Within plasticized material 21.

concomitantly with the initial shaping of the plasticized material 21 into an envelope as described above and throughout the continuous tube manufacture, additional plasticized material 21 is supplied into the inverted cup 19 through the supply pipe 25 to maintain a continuous flow thereof over and around the cup free-edge 29. As illustrated, a substantial length of the feed line 25 is immersed within the bath 17, thus allowing the plasticized material 21 to assume the same temperature as the bath liquid during its delivery into the inverted cup 19.

The envelope of plasticized material which is initially formed is withdrawn from the bath 17 and laced between a pair of nip rolls 45 which are preferably driven at a constant rate. In this manner, a uniform amount of plasticized material 21 is drawn from the trough 19 up through the bath 17 and relative to the confined fluid charge, and is thereby shaped into a tube form as shown at 41. Coagulation or stabilization of the tube wall may be partially or completely effected by the liquid bath as the tube is drawn therethrough. Alternatively, or in combination with this procedure, the tube 41 may be set as it leaves the bath 17 by the atmosphere above the bath 17, or by heated or chilled liquids or gases impinged against the surface thereof, as by an annular nozzle 43. It will be noted that the use of nip rolls 45 as described above causes a pinching or flattening of the tube 41 and thus the gaseous portion 37 of the fluid charge is retained in a confined position. While this procedure is highly desirable when making a flexible tube or casing, it will be understood that conventional pipe draw rolls may be substituted for the nip rolls 45 when a rigid tube is being formed.

Disregarding any shrinkage which may occur during the tube-setting or stabilization stage, the internal diameter of the finished tube will, in general, be equal to the diameter of the surface area of the liquid portion 35' of the confined fluid charge. It will be noted, however, that while the liquid portion 35 assumes the same level as the bath 17 in an equilibrium condition, the upward or longitudinal pull applied to the tube 41 causes the tube to neck radially inward. This counterbalancing of the longitudinal pull on the tube wall thus elevates the level of the liquid portion 35 slightly above that of the bath 17 and reduces its surface area. Aside from employing liquids of different densities in the fluid charge and bath 17, as discussed hereafter, complete control over the internal size of the tube being formed may be exercised by varying either the rate of tube withdrawal by the nip rolls 45 or the volume of the liquid portion 35 of the fluid charge or the distance between the level of the bath 17 and the plasticized material 21 in the trough, or a combination of these factors.

During the formation of both the initial envelope and the continuous tube 41, an annular layer of plasticized material appears to flow along the surface of the confined mass as it is drawn from above the inverted cup 19 and shaped into a tube. The liquid bath 17 and the liquid portion 35 of the contained fluid charge confine the plasticized material 'to a streamlined path, and in effect, cooperate together as a pair of fluid extrusion die lips which hydraulically shape the plasticized material into a tube form. Since the weights of the liquids within and surrounding the tube 41 remain substantially constant, the opposing forces acting on the plasticized material as it is drawn from the accumulated portion thereof above the inverted cup are constant, and thus the tube'41 is formed with a wall of substantially uniform thickness. It will be further noted that the. liquid forces acting on the plasticized material during its streamlined travel insure that any irregularities in the plasticized material will be removed or at least minimized without actually afiecting the tube-forming process or the tube structure.

As heretofore mentioned and in a manner more fully described in my US. Patent 3,031,311, the internal size of the tube can be varied by employing liquids of different densities for the liquid bath 17 and the liquid portion 35 of the fluid charge. With a difference in density existing between the cooperating liquids, the liquid portion 35 of the fluid charge will assume a level at which its weight per unit area is counterbalanced by an equal opposing pressure exerted by the surrounding liquid bath 17. Thus, in an equilibrium condition, the liquid portion 35 of the confined fluid charge presents a relatively small surface area at its uppermost level when it is of less density than the liquid of the bath 17, as shown in FIG URE 3 and thereby provides a tube 41 of smaller internal diameter than is obtained with the liquids heretofore mentioned. On the other hand, a confined fluid charge having a liquid portion 35 of greater density than the liquid of bath 17 presents a relatively large surface area and thereby provides a tube of larger internal size, as shown in FIGURE 4. Assuming that the liquid and gaseous portions of the fluid charges employed in illustrations of FIGURES 2, 3 and 4 are of the same volumes, it will be noted that the liquid portion 35 which is of less density than the liquid of the bath 17 assumes a level which is above that of the bath 17 (FIGURE 3), while the level of a confined liquid portion 35 of greater density is below that of the bath 17 (FIGURE 4). In it will be noted, however, that the tubes of plasticized material in FIGURES 3 and 4 are subjected to the longitudinal pull of the nip rolls 45, and thus the levels of the liquid portions 35 are illustrated as being at slightly higher levels than that which would exist at an equilibrium state, for reasons as heretofore described.

In addition to assisting in floating the initially formed envelope of plasticized material to the bath surface during the initiation of the tube-forming procedure, the gaseous portion 37 of the fluid charge, which is confined within the tube by the liquid portion 35 and the nip rolls 45, serves to prevent collapse of the tube prior to and/ or during its stabilization stage. With plasticized materials which are in a tacky condition when withdrawn from the bath 17, it will be apparent that the confined gaseous portion 37 prevents portions of the internal wall surface from adhering to each other. For example, when employing polypropylene as the plasticized material 21 and a heat-transfer compound, such as Hitec which is available from the E. I du Pont de Nemours and Co., Inc. of Wilmington, Del., as the liquid bath 17 and confined fluid charge 35, the tube 41 which is initially formed may be only partially set as it travels through the bath 17 and can then be maintained in an expanded shape by a confined gas 37, such as air, while it undergoes complete settings as by chilled air. The nature and volume of the confined gas will depend upon various factors such as the chemical character of the plasticized material, the wall thickness of the tube 41 and the particular setting medium used.

When forming tubes which have a rigid structure in their completed state, the fluid charge initially confined Within the mass of plasticized material 21 may consist entirely of liquid. Such liquid charge may be injected into the mass of plasticized material 21 in the same manner as heretofore described and would completely fill the expanded envelope which is initially formed. This envelope would then be withdrawn from the bath 17 to draw plasticized material from the portion thereof which has accumulated above the inverted cup 19 and shape the same into a tube as heretofore described. Conventional pipe draw rolls, not shown, may be substituted for the nip rolls 45 when rigid tubes are being formed. It will be understood that a confined fluid charge consisting entirely of liquid can be employed in making tubes which are either of flexible or rigid character and, if desired, that a fluid charge of liquid and gas may be used in at least initiating the formation of rigid tubes.

The particular liquids used as the bath 17 and the liquid portion 35 of the fluid charge will depend upon various factors such as the chemical character and density of the plasticized material, the size of the tube desired, the rate at which coagulation may be effected if the liquids are to serve as coagulating mediums, and so forth. It will of course be apparent that the liquids employed must be more dense and should not mix or chemically unite with the plasticized material. The term liquid, as heretofore defined, includes a variety of materials from solutions to materials which are in molten condition at the temperature or operation, and thus W 6 melting point salts and metals, such as gallium, may be used if desired.

As heretofore mentioned, the plasticized material appears to flow as an annular layer along the surface of the contained fluid charge as it is drawn from the accumulated portion thereof above the inverted cup 19 and shaped into a tube form. The liquid of the bath 17, when employed as a coagulating medium, will tend to eflect a preliminary setting or stabilization of the surface layer of this accumulated plasticized material, with complete coagulation occurring as the tube of the plasticized material travels through the liquid bath. Alternatively, premature coagulation of the plasticized material may be avoided, for example, by heating the inverted cup 19 with electric coils embedded within its walls.

It is understood that to form flat film the tube is slit longitudinally in one or more places after the tube has been withdrawn from the liquid bath.

While preferred embodiments of the invention have been shown and described, it is to be understood that changes and variations may be made without departing from the spirit and scope of the invention as defined in the appended claims.

I claim:

1. A method making tubes, films and like articles including the steps of retaining a mass of plasticized material within a liquid bath, said lasticized material having a density less than that of said liquid bath, permitting one portion of the plasticized material to float toward the surface of the liquid bath while remaining attached to the mass, injecting a fluid charge including a liquid portion into said one portion of plasticized material to thereby contain the same therein, said liquid bath and fluid charge being immiscible with the plasticized material, drawing the plasticized material through the liquid bath and relative to the contained fluid charge to thereby shape the plasticized material into a tube, and setting the shaped tube.

2. A method of making tubes, films, and like articles including the steps of containing afluid charge including a liquid within a mass of plasticized film-forming material positioned within a liquid bath to expand a portion of the mass, said film-forming material having a density less than that of said liquid bath and being immiscible with the liquid bath and fluid charge, withdrawing the expanded portion of the mass to draw film-forming material through the liquid bath and relative to the contained fluid charge to thereby shape the same into a tube, continuously delivering film-forming material to maintain the mass thereof generally the same, and setting the tube of film-forming material.

3. A method of making tubes, films and like articles including the steps of disposing a mass of plasticized material beneath a generally rigid retainer located within a liquid bath, said plasticized material having a density less than that of said liquid bath' whereby it is buoyant-1y maintained against the underside of said retainer, causing a portion of the plasticized material to flow over the edges of the retainer and accumulate as a mass above the retainer, such accumulated mass remaining attached to the remainder of the plasticized material, injecting a fluid charge including a liquid portion into the mass of plasticized material accumulated above the retainer to thereby contain the same therein, said liquid bath and fluid charge being immiscible with the plasticized material, drawing the plasticized material through the liquid bath and relative to the contained fluid charge to thereby shape the plasticized material into a tube, and setting the tube of plasticized material.

4. A method of making tubes, films and like articles including the steps of disposing a mass of plasticized material within an inverted container having a free edge and located within a liquid bath, said plasticized material having a density less than that of said liquid bath whereby it is buoyantly maintained within the inverter container, causing plasticized material to continuously flow from the container over the free edge thereof and toward the surface of theliquid bath, containing a fluid charge including a liquid portion within the plasticized material which is located above the container, said liquid bath and fluid charge being immiscible with the plasticized material, drawing the plasticized material which flows from the container relative to the contained fluid charge .to thereby shape the plasticized material into a tube, and setting the tube of plasticized material. 7

5. A method as defined in claim 4 wherein the fluid charge is of a density at least equal to that of said liquid bath.

6. A method as defined in claim 4 wherein said fluid charge is of a density not greater than that of said liquid bath.

7. A method as defined in claim 4 wherein the fluid charge is composed entirely of liquid.

8. Apparatus for making tubing including a tank for holding a liquid bath, a generally rigid, annular retainer positioned within said tank for preventing a plasticized material which is buoyant in the liquid bath from floating ROBERT F. WHITE,

to the surface thereof, means for delivering plasticized material to the underside of said retainer whereby the plasticized material flows about the edge of the retainer and accumulates as a mass along the upper side thereof, means for injecting a fluid charge into the mass of plasticized material to expand a portion thereof, and means for withdrawing the expanded portion of the mass from said tank to draw plasticized material relative to the fluid charge and shape the same into a tube.

9. Apparatus as defined in claim 8 wherein said ret-ainer is an inverted container having a free edge.

10. Apparatus as defined in claim 8 wherein said retainer is an inverted container having an annular, smooth free edge.

References Cited UNITED STATES PATENTS 2,987,776 6/ 1961 Miller et a1. 264-95 X 3,013,311 12/1961 Meissner 26495 X Primary Examiner.

A. R. NOE, Assistant Examiner. 

1. A METHOD MAKING TUBES, FILMS AND LIKE ARTICLES INCLUDING THE STEPS OF RETAINING A MASS OF PLASTICIZED MATERIAL WITHIN A LIQUID BATH, SAID PLASTICIZED MATERIAL HAVING A DENSITY LESS THAN THAT OF SAID LIQUID BATH, PERMITTING ONE PORTION OF THE PLASTICIZED MATERIAL TO FLOAT TOWARD THE SURFACE OF THE LIQUID BATH WHILE REMAINING ATTACHED TO THE MASS, INJECTING A FLUID CHARGE INCLUDING A LIQUID PORTION INTO SAID ONE PORTION OF PLASTICIZED MATERIAL TO THEREBY CONTAIN THE SAME THEREIN, SAID LIQUID BATH AND FLUID CHARGE BEING IMMISCIBLE WITH THE PLASTICIZED MATERIAL, DRAWING THE PLASTICIZED MATERIAL THROUGH THE LIQUID BATH AND RELATIVE TO THE CONTAINED FLUID CHARGE TO THEREBY SHAPE THE PLASTICIZED MATERIAL INTO A TUBE, AND SETTING THE SHAPED TUBE. 